The truth

The truth that Gene says in the last chapter is that he envies Finny. He envies him to a point that he can’t say they are friends anymore. Near the beginning when Finny gets then out of trouble, Gene says that little envy is ok. This comment is false because he envied his friend and now it got a lot worse. Because he is friends with Finny, he feels obligated to act cool like Finny. This is why he jumps off the tree with Finny, and he always wrestles with him.